Prevent sign-extension during byte array to string conversion

Question

The BYTEMASK flag in the sample code keeps the value from being signed-extended when it's converted to an int. How is this flag preventing the conversion form being sign-extended?

private final static int BYTEMASK = 0xFF;

private static String byteArrayToDecimalString(byte[] bArray) {
        StringBuilder rtn = new StringBuilder();
        for(byte b : bArray) 
            rtn.append(b & BYTEMASK).append(" ");
        return rtn.toString();
    }

The value *is* sign-extended. But then the mask removes the sign extension. — Oliver Charlesworth, Jan 01 '18 at 12:34
It does becase the sign bit (1), when binary-anded with 0, becomes 0. Because 1 & 0 is 0. — JB Nizet, Jan 01 '18 at 12:36

score 1 · Accepted Answer · answered Jan 01 '18 at 12:40

1

As others have already mentioned in comments, the bytemask does not prevent the sign extension, instead it undoes it. For example:

0x80 -- sign extend -> 0xffffff80 -- mask with 0xff -> 0x00000080

answered Jan 01 '18 at 12:40

Henry

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Thanks for the feedback. I'm stepping through the code in the debugger to understand the process. – dcrearer Jan 01 '18 at 12:51

Prevent sign-extension during byte array to string conversion

1 Answers1